Many authors tried to observe the major parameters influencing the dry-heating viral inactivation. The objective is to define a physicochemical parameter which would allow to predict whether or not a given treatment is suitable for the solid material to be treated, i.e. whether or not the process will inactivate the virus to a sufficient extent while preserving a satisfactory stability of the product. Moreover, it would be extremely interesting if this parameter could be adjustable to favour either viral inactivation or product stability.
The viral reduction factor of a viral inactivation process is defined as the factor by which the viral inactivation by dry heating is reduced, i.e. the base10 logarithm of the ratio of the viral inactivation by dry heating before the inactivation step and the viral inactivation by dry heating after the inactivation step.
The moisture content is defined as the weight quantity of matter per 100 g of the product. This is why it is expressed as a percentage of the overall weight. The traditional measure method consists in determining the decrease in weight of the product after heating at a temperature of over 100° C. until its weight remains constant.
Wilkommen et al. (Paul Ehrlich Institute) showed that, for lyophilisates containing a poor moisture level (<0.8%), Hepatitis A Virus (HAV) reduction factors obtained by heating at 80° C. for 72 hours range from 0 to 0.4 log 10, whereas for lyophilisates with a relatively high moisture level (> 0.8%), Hepatitis A virus reduction factors obtained in the same conditions are greater or equal to 4.3 log 10.
Bunch et al. (Alpha Therapeutic Corporation) showed that, for two samples of a recombinant Factor VIII Hepatitis A Virus reduction factor (≧6.9 log 10) when heated at 80° C. for 72 hours.
Roberts P L et al. (Biologicals [2000] September; 28(3): 185-8 Comparison of the Inactivation of Canine and Bovine Parvovirus by Freeze-Drying and Dry-Heat Treatment in Two High-Purity Factor VIII Concentrates) showed the influence of the formulation of the biological product and of the resistance of the virus through the viral inactivation of two parvoviruses (bovine and canine) when two lyophilised formulations of a Factor VIII concentrate were heated at 80° C. for 72 hours.
Hart H F et al. (Vox Sang [1994] 67(4): 345-50 Effect of Terminal (Dry) Heat Treatment on Non-Enveloped Viruses in Coagulation Factor Concentrates) obtained the same Hepatitis A Virus reduction factor in Factor VIII lyophilisates heated at 80° C. for 24 hours or 90° C. for 2 hours.
Tomokiyo et al. (Vox Sang [2003] January; 84(1): 54-64 Large-Scale Production and Properties of Human Plasma-Derived Activated Factor VII Concentrate) showed, through inactivation of different viruses: CMV (Cytomegalovirus), HTV (Human Immunodeficiency Virus), BVDV (Bovine Viral Diarrhoea Virus Poliovirus), PPV (Porcine Parvovirus) in lyophilisates of Factor VIIa, that viral inactivation in lyophilisates is possible at 65° C. Heating at 65° C. for 96 hours of products with a moisture level of <1.7% shows vital reduction factors of >4 log 10 for all the viruses apart from PPV.
Patent Application EP 0 844 005 discloses that it is the residual moisture content of the desiccated biological product to be treated that is the critical element in the efficacy of viral inactivation through a dry-heating process at 80° C. for 72-77 hours. The viruses tested were HAV, Porcine Parvovirus and Pseudorabies Virus. The inventors showed that the residual moisture must be greater or equal to 0.8% to reach a viral reduction factor of ≧4 log 10 using this process. For residual moisture ≦0.8%, the mean viral reduction factor is 0.12 log 10.